Aerodynamics (was: fatality Poland 10 June 2023 WS possible hard opening)

45 minutes ago, olofscience said:

When you pull the yoke of an aircraft, nothing happens on the (front) wing. If I were to use your words - no release of mechanization happens.

 

Lift coefficient would still increase though.

Yes, on many aircraft, with a sufficient increase vertical angle and/ or decrease in speed, the front slats fall out automatically. It is in order to increase the lifting force. Deflecting the steering wheel towards itself can both increase and decrease lift force, depending on the current mode - it increases drag to a greater extent, and changes the thrust vector of the engine.

Drag is a tool for creating lift, and there is no engine thrust in parachutes, there are no slats, there are no flaps that increase the wing area, the planning mode is slightly regulated by risers and toggle lines (analogous to ailerons), at the end of landing. Therefore, the aerodynamics of the aircraft is low applicable to parachutes.

50 minutes ago, billvon said:

Nope.  During normal flight, lift is increased by increasing the angle of attack.  This is done by deflecting the elevators on the back of the horizontal stabilizers using the yoke/stick.  Nothing to do with "mechanization" on the wing.

What you are talking about - flaps and slats - are only used during takeoff and landing, to reduce stall speed so that the aircraft can take off/land at a slower airspeed.

But don't take my word for it.  Take a flying lesson and see for yourself.  Or just look out the window of an airplane next time you are in one.

The question is what is the reason - the wind or the swaying trees? The first thing that changes when the nose of the aircraft is lift is the angle of thrust of the engines.

The lifting force decreases with decreasing speed, so you have to increase it by releasing mechanization. During takeoff and landing, when parachutists jump off, when engines lose thrust, etc.

I trust your experience as a practitioner, and you don't have to doubt the theory if it allows you to make the right decisions. Even if she's wrong about something...

On 6/18/2024 at 11:53 PM, TampaPete said:

FADE IN:

EXT. PEASANT TOWN SQUARE – DAY

A PEASANT GROUP runs toward the TOWN SQUARE dragging a YOUNG WOMAN dressed as a WING. SIR BEDEVERE, tending to physics experiments, releases a nuclear powered ornithopter tied to a coconut.

PEASANT GROUP

(Shouting)

"We found a wing, she’s a wiiing fling her."

BEDEVERE

(addressing the peasants)

"How do you knoooooow she’s a wing?"

PEASANT GROUP

(Shouting)

" ‘Cause she looks like one."

"FLIIIIIING her."

YOUNG WOMAN

"I’m not a wing. They did this to me."

"These aren’t my A lines."

Bedevere addresses the peasants.

BEDEVERE

"Did you do this to her?"

PEASANT GROUP

"No… no… no… yes… no."

PEASANT 1

"We did do the A lines."

"And the d-bag."

(pause)

"But she does have an air lock."

PEASANT GROUP

(Shouting)

"FLIIIIING her!"

BEDEVERE

"There are ways to tell if she is a wing."

The peasants look confused.  

BEDEVERE

"What else can be flung like a wing?"

PEASANT GROUP

"Churches… marshmallows… navel lint… Mozhaisky’s airplane…"

KING ARTHUR watches the goings on from the side.  

KING ARTHUR

"A piano… flung from a trebuchet."

All turn to look at Arthur. Bedevere, in great amazement, exclaims…

BEDEVERE

"Exactly!"

PEASANT 1

"So… if she can be flung…"

Peasant 1 strains to find the logic.

"As far as a piano……"

PEASANT GROUP

(Shouting)

"She’s a wing… fliiiing her."

BEDEVERE

"We’ll use my largest trebuchet."

Unfortunately, at this point the illogic of the physics takes hold causing the film to be quickly burned by the bulb and break. Thus, just like how many licks it takes to get to the center of a Tootsie Roll Pop the world will never know how far a Wing can be flung from a trebuchet.

9 hours ago, Veis said:

Yes, on many aircraft, with a sufficient increase vertical angle and/ or decrease in speed, the front slats fall out automatically.

Most aircraft don't have front slats. Even fewer have automatically deployed slats.

with all of these knowledgeable folks arguing about what causes lift, it amazes me even more that airplanes can fly.  has to be like i called it before:  magic.  otherwise all the fine folks with all that knowledge gleaned in school, textbooks, and the seats of airplanes would know how it works and agree on the physics, presumably at least. 

3 hours ago, sfzombie13 said:

with all of these knowledgeable folks arguing about what causes lift, it amazes me even more that airplanes can fly.  has to be like i called it before:  magic.  otherwise all the fine folks with all that knowledge gleaned in school, textbooks, and the seats of airplanes would know how it works and agree on the physics, presumably at least. 

3 minutes ago, billvon said:

It has to do with your previous question: "where did you read that an increase in the angle of attack leads to an increase in lift?"

Sometimes we call that "flaring".

18 hours ago, Veis said:

where did you read that an increase in the angle of attack leads to an increase in lift?

https://www.google.com/search?client=firefox-b-d&q=increase+in+the+angle+of+attack+leads+to+an+increase+in+lift

Smithsonian institute https://howthingsfly.si.edu/aerodynamics/factors-affecting-lift

Nasa https://www.grc.nasa.gov/WWW/K-12/FoilSim/Manual/fsim0004.htm

FAA https://www.faa.gov/sites/faa.gov/files/2022-01/Angle of Attack Awareness.pdf

Skybrary https://skybrary.aero/articles/angle-attack-aoa

Pilot institute https://pilotinstitute.com/what-is-angle-of-attack/

Cambridge University https://www3.eng.cam.ac.uk/outreach/Project-resources/Wind-turbine/howwingswork.pdf

Hundreds of research papers like this one https://www.researchgate.net/publication/339210108_Effect_of_Angle_of_Attack_on_Lift_Drag_Pitching_Moment_and_Pressure_Distribution_of_NACA_4415_Wing

Including this one explaining how the effect of mechanization of the wing is to create lift by moving both the cord and angle of attack on the wing in its new configuration

https://www.researchgate.net/figure/When-a-plain-flap-is-deflected-the-increase-in-lift-is-due-to-an-effective-increase-in_fig3_273923634

Thousands of other similar results if you so much as dared to look for them instead of just making it up

On 6/20/2024 at 1:31 PM, pchapman said:

Getting aerodynamic principles just right, and explaining them correctly,  is quite tricky. There are plenty of ways to explain something that are "sorta kinda right in some circumstances, for the example being given, but not sufficiently correct to really explain most of the possible situations". And this particular discussion has been messed up by one participant not having really good command of the English language. Not his fault, but makes explanations and interpretations even more confusing & sketchy & vague.

I'll certainly disagree with Veis on a lot of his aerodynamics. Although I do agree that the Kutta condition or Kutta-Joukowski don't imply that neighbouring air molecules, one going over and one going under an airfoil, need to meet up again at the trailing edge. That just isn't true. So, billvon, I don't think that is a useful part of how to describe lift.

I'll wimp out from wading too far into this, as writing a good textbook explanation of lift is hard. But I'd say:

1. Lift comes from pushing air down. [Circulation in other words, if doing Kutta-Joukowski integration around the whole airfoil stuff]
Edit: That's simple Newton's laws stuff, or force diagrams. Pushing air down means you have pushed up on the wing.

2. You can do that with a flat plate, the so-called barn door, at some angle of attack, catching the air. No curved airfoil needed. But, it is a very inefficient way to make lift, as there's a ton of drag for the lift being produced.  (At the sizes and speeds we are talking about. Things are different at the sizes & speeds of paper airplanes and insects. [Small Reynolds numbers ])

3. Airfoils happen to be a shape that can make lift, while still being really low drag. Very efficient, that's  why we use them.

4. There is some pressure pushing up on the bottom of airfoils if at enough angle of attack. [This gets complex and depends on exact shape & angle]

4. But most of the lift comes from the top: The way air works is that it speeds up and lowers pressure when moving around a gently curved surface. That's where the Bernoulli stuff come into play.  That provides most of the lift of an airfoil.

5. But the air can't turn too sudden of a corner. So at too high an angle of attack, the air starts to separate from the surface of the wing and turns into a swirling chaotic mess of waves and vortexes. The airfoil has stalled. Lift starts to decrease* but drag is massively up, so you no longer have an efficient airfoil and your airplane or parachute is probably going to start dropping suddenly (assuming we are talking about roughly horizontal flight), leading to even higher angle of attack and even lousier flying.
 

*[Edit: Duh somehow I said it was still increasing. Which isn't true for a regular airfoil after the stall. What I should have said is that one can have very low aspect ratio aircraft, or aircraft with strakes, or a wingsuit, or something, where there isn't a simple clean stall. Parts of the wing may not be working efficiently, and there's increasing drag, but lift from say vortexes can keep on rising past say 15 degrees to say 40 degrees angle of attack. The concept of "the stall" isn't as clear cut any more.]

If you want to talk about vortex lift, look at delta-winged jet fighters, Concorde and the swept-wing gliders built by Withold Kasper. This is an obscure corner of aerodynamics that is not relevant to Ram-air parachutes with straight leading edges.

At steep angles-of-arrack the entire leading edge acts like a giant wing-tip and generates large wing-tip vortices. Those WTV generate a bit of lift and massive amounts of drag.

Yes, it is possible to fly on only vortex lift, but VL is massively “draggy.” Only high-powered jets can do it and they can only do it for a few minutes. Simply VLis so draggy that un-powered you develop horrendous rates of descent. Only the most powerful jet fighters can climb while in VL. It was possible to fly the Concorde so low and so slow that it could not climb out of the VL corner. That is why Concorde carried plenty of power during approach and noise complaints were one of the reasons that Concorde retired. Boeing’s 727 had similar drag problems when leading edge flaps were lowered. Yes LE flaps generated plenty of lift, but they also generated LOTS OR Drag, hence the need to carry so much power (to reduce rate-of-descent) during landing approaches. Those LOUD straight jet engines generated too much NOISE which prompted many noise complaints. One of 727 hush-kits reduced LE flap angles to reduce drag and reduce rate-of-descent.

On 6/24/2024 at 9:50 PM, riggerrob said:

1. Lift comes from pushing air down.

All theories based on pushing air down give an underestimate and lost relevance even before the beginning of the twentieth century.

For low-speed wings, the lower surface is now mainly a means of stabilizing and providing feedback.

Quote

 But most of the lift comes from the top: The way air works is that it speeds up and lowers pressure when moving around a gently curved surface.

Explanations that do not involve the mass of air and the movement of this mass, with an increase and decrease in density in significant volumes, and the interaction of these volumes with each other are also unworkable.

Kutta-Zhukovsky works, especially when integrating by volume - but it is descriptive in nature, does not affect the causal relationship of the occurrence of lifting force. Kutta-Zhukovsky is a statistic of the frame of reference associated with the wing and therefore indifferent to the position in space. But at the same time, it does not deny in any way that the lifting force changes from this position.

On 6/21/2024 at 8:29 PM, GoneCodFishing said:

Hundreds of research papers

It doesn't work that way. Give specific quotes.

In addition, I would like to draw your attention to the fact that parachutes are balancing craft, and attempts to change the angle of attack with the help of controls lead to a change in the alignment of the suspended mass.